The two new species are members of a group called parapithecoids, or possible "stem" anthropoidsearly creatures from which the subsequent crown anthropoid line, including humans, arose.

The new species help fill in the gap between later anthropoids and the oldest undisputed anthropoid: Called Algeripithecus, it lived around 45 million years ago and was found in present-day Algeria.

Seiffert's analysis also suggests that a 57-million-year-old primate known as Altiatlasiuspreviously discovered in Moroccois an anthropoid.

While crown anthropoids may have originated in Africa, the most likely place of origin for even older stem anthropoids is in Asia. (Stem anthropoids are the first species to branch off on the anthropoid side of the family tree after their split with tarsiers, a genus of nocturnal primates.)

"Possible fossil anthropoids, such as eosimiids, as well as living and extinct tarsiers and a number of other, more distant primate relatives appear to have originated [in Asia]," Seiffert said.

But fundamental questions remain to be answered about anthropoid origins in Asia and Africa. The early and middle Eocene epoch (55 to 40 million years ago) was a period of active intercontinental exchange of land mammals between Asia and Africa.

"From the most recent data, it is now accepted that anthropoids originated in Asia," said Jean-Jacques Jaeger, a paleontologist at France's University of Montpellier, who wrote an accompanying commentary in Science.

"But when did they immigrate into Africa?" Jaeger said. "This is still a point of hectic debate."